Wireless power transfer systems (e.g., inductive charging systems for electric vehicles) may include a ground-based wireless power transmitter (e.g., a base pad, base wireless charging system, or some other wireless power transfer device including a coupler (e.g., base coupler)) configured to emit a wireless power field to a wireless power receiver (e.g., a vehicle pad, an electric vehicle wireless charging unit, or some other wireless power receiving device including a coupler (e.g., vehicle coupler)) configured to receive the wireless power field on the bottom of the vehicle. In such wireless power transfer systems, the space between the wireless power transmitter on the ground and the wireless power receiver on the vehicle may be open and accessible by foreign objects. For example, foreign objects may accidentally or intentionally be positioned in the space between the wireless power transmitter and the wireless power receiver. Where the foreign object is conducting and/or ferromagnetic (e.g., a metallic object, such as a paper clip, screw, etc.)), when the foreign object is exposed to the wireless charging field between the wireless power transmitter and the wireless power receiver, it may reach high temperatures (e.g., over 200 degrees C.), for example due to eddy current and hysteresis effects caused by the wireless charging field, if flux density levels exceed certain critical levels. The high temperatures the foreign object may potentially reach may damage the wireless power transmitter. For example, the foreign object may sit on the wireless power transmitter and cause portions of the wireless power transmitter to melt or burn, or may itself melt into the wireless power transmitter. Further, detecting the foreign object using certain foreign object detection (FOD) techniques may not be feasible, such as due to the object being small and difficult to detect, or may be too costly. Accordingly, a method and apparatus for detecting foreign objects as described is desirable.